Improving the dimensional stability of round bamboo by environment-friendly modified rosin

Abstract

Round bamboo is an environment-friendly and sustainable building, construction, and furniture material. It presents several advantages, such as high strength-to-weight ratio, pliability, and simple processing technology. However, natural round bamboo has inferior dimensional stability and is difficult to modify because of the hydrophobic substance on its outer layer. In this study, we designed a simple and efficient alkali pretreatment method (6 % NaOH treatment), which could effectively remove the hydrophobic layer from the bamboo surface, as well as significantly improve its permeability for the subsequent impregnation treatment. Round bamboo was impregnated with epoxy-modified rosin and natural rosin with different concentrations. Results showed that parts of the epoxy-modified rosin occupied the cell lumens of the bamboo, even filling the nanopores of cell walls and intercellular spaces (the pore volume of the round bamboo decreased by 84.76 % in 10–140 nm compared with the natural rosin) to exhibit improved dimensional stability (anti-swelling efficiency increased by 33.74 %) and hydrophobicity (contact angle increased, and water absorption decreased by 24.73 %). After impregnating the round bamboo, the modified rosin was physically filled into the vessels, parenchyma cells, and other structures. Meanwhile, the peak at 908 cm−1 indicates the disappearance of the the CO stretching vibration of the epoxy ring, confirming the occurrence of a reaction between the modified rosin and hydrophilic groups in the round bamboo. Therefore, impregnation with modified rosin can markedly improve the dimensional stability of round bamboo. The modified round bamboo exhibits considerable potential for application as a green structural material in an outdoor environment or a special environment with highly variable humidity.